1. Field of the Invention
The present invention relates to the improvement of sound characteristics in an audio system.
2. Description of the Related Art
Various techniques have been developed to enhance the perceived quality of audio signals. One of these techniques is dynamic range compression (DRC), which is a process that manipulates the dynamic range of an audio signal. Compression may be used during broadcasting in order to alter the perceived volume of audio.
Compression may be achieved by use of a compressor, which is sometimes referred to as an automatic volume control. Compression may reduce the level of loud sounds over a certain threshold, while the level of quiet sounds is not reduced. Thus, compression may reduce the dynamic range of an audio signal. Compression may be performed to improve aesthetics of the sound, to accommodate technical limitations of audio equipment, or to improve the audibility of audio signals in noisy environments.
Quiet sounds may be overpowered in a noisy environment, making them difficult to hear. That is, the background noise can drown out quiet sounds. Reducing the sound level for loud sounds may result in the quiet sounds being inaudible. Conversely, increasing the sound level for quiet sounds may result in the loud sounds being uncomfortably loud. Compression may be used to make both the quiet and loud parts of an audio signal audible at a comfortable level at the same time. Compression reduces the level of the loud sounds, but does not reduce the level of the quiet sounds. Thus, the sound level may be raised such that the quiet sounds are audible, but the loud sounds are not too loud.
The length of time required for a compressor to respond to changes in input level is known as attack time. The length of time required for the sound level to fall from a maximum level to a steady state level is referred to as decay time. The length of time the audio level remains at the steady state level is referred to as the hold time. The length of time required for a compressor to return to no gain reduction after the input level falls below a steady state or threshold level is known as release time. In many compressors, the use may adjust the attack and release times. Some compressors, however, have fixed attack and release times that are determined by the circuit design and that cannot be adjusted by the user. In some cases, the attack and release times are “automatic” or “program dependent.” That is, the times change depending upon the input signal. The loudness pattern of the source material may be modified by the compressor, the compressor may change the character of the signal in very noticeable ways under certain settings.
Accordingly, what is neither anticipated nor obvious in view of the prior art is an improved apparatus and method of source level matching both when operating within a single audio medium and when switching between audio media.